Propeller for outboard motor

ABSTRACT

An outboard motor is generally mounted to a hull of a boat, for example, and includes a propeller fixed to a rear portion of a propeller shaft pivotally supported in an anteroposterior direction of the hull on a lower portion of the outboard motor. The propeller includes a cylindrically formed propeller hub, and blades provided radially on an outer side of the propeller hub, and having surfaces of the blades, including blade body and root portion, to which a shot-peening treatment is applied. The propeller may be formed of a metal material having a surface on which an oxide coating is formed by heating the metal material.

PRIORITY CLAIM

This patent application claims priority to Japanese Patent Application No. 2011-035465, filed 22 Feb. 2011, and Japanese Patent Application No. 2011-038194, filed 24 Feb. 2011, the disclosures of which are incorporated herein by reference in their entirety.

BACKGROUND

1. Field

Disclosed embodiments relate to a propeller for an outboard motor which mounted to a hull of a boat, for example, and the propeller is fixed to a rear portion of a propeller shaft in order to propel the outboard motor by driving an engine.

2. Related Art

Usually, a propeller is provided on a rear portion of a propeller shaft in an outboard motor in order to obtain a propelling force of a hull of a boat, for example, and when an engine of the outboard motor is driven, the propeller is rotated with a propeller shaft in a water (for example, sea water) through a drive shaft and a bevel gear arrangement.

Further, regarding the propeller for an outboard motor, a water flow incident to one blade and an angle of a blade of the propeller (attack angle) are changed in accordance with rotation (rotational motion) around the propeller shaft during a time when an outboard motor is driven for running a boat to which the outboard motor is mounted, and thus, a thrust force generated in one blade is changed in accordance with the rotation angle. Therefore, a stress repeatedly occurs at a root portion of each blade, and if the strength of the blade is not sufficient, the blade is likely to break at the root portion. In view of such defect, in a conventional art, the strength of the propeller has been reinforced by increasing the thickness of the root of the blade of the propeller or of the blade itself, for example as disclosed in Patent Documents 1 to 3 (Japanese Patent Application Laid-Open Publication Nos. 2008-111499, 2008-230337, and 2010-264905.

However, in the above-described prior-art propeller for an outboard motor, the thickness of the root of the blade of the propeller or of the blade itself is increased and thus, the weight of the propeller is increased, and hence, a rotation moment is raised, which may result in causing of a problem of an increased load to a power transmission portion such as a shaft or a gear or defective casting.

Furthermore, if the outboard motor is driven at a high speed and a boat having a hull to which the outboard motor is mounted is moved, erosion occurs in the vicinity of the root portion of the blade constituting a negative pressure surface or a cup constituting a positive pressure surface due to cavitation generated from the distal end of the blade, and there is a concern that the blade might break. As measures against the problem, in the case of a propeller made of aluminum, anodized oxide coating is applied to the surface in order to improve surface hardness, but the surface hardness does not become sufficiently high with respect to high construction cost thereof, and unfortunately, an effect to prevent breakage is low, thus being disadvantageous.

Moreover, in the above prior technology, since surface working is applied to the propeller for an outboard motor by buffing treatment after manufacture through die-casting or precision casting, and thus, unfortunately, a hairline generated on the surface might cause a crack or erosion.

In another viewpoint of the above prior technology, in the conventional structure of the type mentioned above, in order to prevent corrosion in the use under water, the propeller is formed by using a anti-corrosion material or substance, and after the die-casting or precision forging, coating is applied to the surface of the propeller according to desire or taste of a user to thereby improve an outer appearance as a product.

However, in such structure, there is a fear of going aground or contacting to a floating substance, which may result in peeling-off surface coating to thereby damage outer appearance or configuration.

SUMMARY

Disclosed embodiments provide a propeller for an outboard motor capable of improving performances through alleviation of a load to a power transmission portion and also improving durability through prevention of occurrence of the defective casting or erosion.

One disclosed embodiment provides a propeller for an outboard motor capable of improving anti-corrosion property and peel-off resisting performance as well as improvement as products.

Disclosed embodiments provide a propeller for an outboard motor fixed to a rear portion of a propeller shaft pivotally supported in an anteroposterior direction of a hull to which the outboard motor is mounted on a lower portion of the outboard motor, the propeller including a cylindrically formed propeller hub, and a plurality of blades provided radially on an outer side of the propeller hub, and having surfaces of the blades to which a shot-peening treatment is applied.

In one disclosed embodiment, the following disclosed example may be provided.

Each of blades may have a blade body and a root portion having a surface to at least one of which the shot-peening treatment may be applied.

It may be desired that the shot-peening treatment for mirror finishing is applied.

It may be desired that the metal member forming the propeller contains at least one material of titanium, stainless steel and copper. The metal member forming the propeller may be subjected to mirror finishing by a shot-peening treatment before the oxide coating is formed.

According to the propeller for an outboard motor disclosed above, various excellent advantages can be obtained that the performances can be improved through alleviation of a load to a power transmitting component, durability can be improved through prevention of occurrence of defective casting or erosion and the like. Furthermore, anti-corrosion property and anti-peeling property can be also improved, thus propellers as products improved in quality can be provided.

The nature and further characteristic features of the present invention will be made clearer from the following descriptions with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a right side view illustrating an entire structure of an outboard motor, partially in section, provided with a propeller for an outboard motor; and

FIG. 2 is an illustrated side view of the propeller for an outboard motor.

DESCRIPTION OF THE DISCLOSED EMBODIMENTS

Disclosed embodiments will be described with reference to the accompanying drawings. It is further to be noted that terms “upper”, “lower”, “right”, “left” and like terms representing direction or like are used herein with reference to the illustration of the drawings or in a state of the outboard motor mounted to a hull of a boat, for example.

First, an entire structure of an outboard motor 1 will be described by referring to FIG. 1.

In an external appearance of an outboard motor 1, the outboard motor 1 has a major configuration or portion including an engine cover 2 provided on an upper portion of the outboard motor 1 and having vertically dividable structure, a drive-shaft housing 3 provided below the engine cover 2, and a gear housing 4 fixed to a lower end portion of the drive-shaft housing 3. The drive-shaft housing 3 and the gear housing 4 constitute a lower unit 5 of the outboard motor 1.

A steering bracket 6 is provided in front of the engine cover 2 (right side on FIG. 1, i.e., on a side near a hull of a boat body, for example), and the steering bracket 6 is provided with a pilot shaft 7 extending in the perpendicularly downward direction. A handle bracket 8 is fixed to a front end portion of the steering bracket 6, and a tiller handle 10 is supported rotatably in the vertical direction on the front end portion of the handle bracket 8.

A clamp bracket 11 which fixes the outboard motor 1 to a hull, not shown, is provided below the steering bracket 6, and a swivel bracket 13 is supported rotatably in the vertical direction through a tilt shaft 12 on the clamp bracket 11.

An engine 14 is housed within the engine cover 2. The engine 14 is, for example, an OHC-type water-cooling multi-cylinder engine, in which an oil pan 15 is fixed to a lower end portion of the engine 14, and a starter motor 16 is fixed to a front end portion of the engine 14.

A carburetor 17 is fixed to a side portion of the engine 14, and one end of a throttle cable 19 is connected to the carburetor 17 through a drum 18, while the other end of the throttle cable 19 is connected to the tiller handle 10.

A crank shaft, not shown, is pivotally supported in the substantially perpendicular direction on the engine 14, and a drive shaft 9 is coupled to the crank shaft. The drive shaft 9 is provided so as to penetrate the drive-shaft housing 3 in the vertical direction, and a drive gear 20 is fixed on a lower end portion of the drive shaft 9 so as to face the inside of the gear housing 4.

A propeller shaft 22 is pivotally supported in the anteroposterior direction (longitudinal direction of a hull) in the gear housing 4. A forward driven gear 23 and a backward (reversed) driven gear 24 are provided rotatably with respect to the propeller shaft 22 on a front portion of the propeller shaft 22. The forward driven gear 23 is always meshed with a front portion of the drive gear 20, while the backward driven gear 24 is always meshed with a rear portion of the drive gear 20.

A propeller 21 is fixed to a rear portion of the propeller shaft 22. The details of the propeller 21 will be described herein later.

The propeller shaft 22 is connected to the tiller handle 10 through a shift mechanism 25.

The shift mechanism 25 includes: a shift slider 26 attached to a front portion of the tiller handle 10 capable of advancing/retreating in the anteroposterior direction; a pair of upper and lower shift cables 27 having one ends connected to the shift slider 26 through a shift drum, not shown, or the like, a clutch shaft 28 to which the other ends of the pair of upper and lower shift cables 27 are connected; a clutch rod 30 connected to the clutch shaft 28 at the upper end portion and penetrating through the pilot shaft 7; a shift rod 32 coupled to a lower end portion of the clutch rod 30 at the upper end portion through a pair of connectors 31; a shift cam 33 provided on a lower end portion of the shift rod 32; a push rod 34 provided in contact with the shift cam 33 on the front end portion; and a shifter dog 35 coupled to a rear end portion of the push rod 34 and provided on the propeller shaft 22.

The clutch rod 30 is provided on the side of the engine 14 of the outboard motor 1 (upper side in the illustration of the embodiment), and the shift rod 32 is provided on the side of the lower unit 5 of the outboard motor 1 (lower side in the illustration). The clutch rod 30 and the shift rod 32 have the same outer diameter.

A step-shaped contact surface 36 is provided on a rear surface of the shift cam 33. The push rod 34 is urged by a spring, not shown, forward so as to be brought into contact with the contact surface 36 of the shift cam 33. The shifter dog 35 is interposed between the forward driven gear 23 and the backward driven gear 24 and is provided to be integrally rotatable with the propeller shaft 22 and movable in the anteroposterior direction thereof.

In the outboard motor 1 of the structure or configuration mentioned above, when the engine 14 is driven, rotation of the crank shaft of the engine 14 is transmitted to the drive shaft 9 to rotate the same. According to the rotation of the drive shaft, the drive gear 20 provided on the lower end portion of the drive shaft 9 is hence rotated, and the forward driven gear 23 and the backward driven gear 24 always meshed with the drive gear 20 are then rotated in the directions opposite to each other.

In the state where the engine 14 is driven as described above, if the shift slider 26 provided on the tiller handle 10 is moved back and forth, the shift cam 33 is driven through the shift cables 27, the clutch shaft 28, the clutch rod 30, and the shift rod 32, and hence, the shift cam 33 is moved up and down. The contact position on the contact surface 36 of the shift cam 33 with the push rod 34 is changed by the up-and-down movement of the shift cam 33, and the push rod 34 is moved back and forth. According to such movement, the shifter dog 35 is moved back and forth between the contact position with the forward driven gear 23 and the contact position with the backward driven gear 24.

When the shifter dog 35 is moved forward to the contact position with the forward driven gear 23 by a manipulation of the shift slider 26, the rotation of the drive gear 20 is transmitted to the propeller shaft 22 through the forward driven gear 23 and the shifter dog 35, and the propeller shaft 22 and the propeller 21 are rotated forward, thereby moving the hull forward.

On the other hand, when the shifter dog 35 is moved backward to the contact position with the backward driven gear 24 by the manipulation of the shift slider 26, the rotation of the drive gear 20 is transmitted to the propeller shaft 22 through the backward driven gear 24 and the shifter dog 35, and the propeller shaft 22 and the propeller 21 are rotated backward, thereby moving the hull backward.

Further, when the shifter dog 35 is moved to an intermediate position not in contact with the forward driven gear 23 or the backward driven gear 24 by the manipulation of the shift slider 26, the drive shaft 9 takes a neutral position and the rotation of the drive shaft 9 is not transmitted to the propeller shaft 22, and thus, the hull is stopped.

According to the manner mentioned above, the shift-change is performed among forward rotating position, backward rotating position, and neutral state position, and movement of the hull is switched among going forward, going backward and stop positions.

Hereunder, the propeller 21 for an outboard motor according to disclosed embodiments will be described with reference to FIGS. 1 and 2.

The propeller 21 for an outboard motor is generally made of metal material such as aluminum, stainless steel, titanium, and the like and composed of a propeller hub 40 having a double-cylindrical structure formed by integrally joining a concentric inner cylindrical body 37 and an outer cylindrical body 38 by means of a plurality of radial ribs 39, and three blades 41 arranged radially on the outside of the outer cylindrical body 38. A coupling cylinder 42 made of rubber is press-fitted into the inner cylindrical body 37, and the propeller 21 is tightly attached to the propeller shaft 22 by fitting the coupling cylinder 42 in the rear portion of the propeller shaft 22.

When such propeller 21 for an outboard motor is to be manufactured, after the propeller hub 40 and each of the blades 41 are integrally formed by casting, a shot-peening treatment is applied to the surface of the propeller 21. In this shot-peening treatment, small steel balls, each of approximately 0.05 to several mm, are blown to the surface of the propeller 21, which is a surface to be worked, at a speed of approximately 40 to several hundred m/s. At this time, the shot-peening treatment may be applied to the whole surface of each of blades 41 of the propeller 21 but may be applied only to a root portion 43 of each of the blades 41 to which a load is specifically applied while the outboard motor 1 is operated.

Further, it is to be noted that the term “blade 41” is used herein such that it may include a blade body (41) and the root portion 43.

Subsequently, in addition to or instead of the above-described shot-peening treatment, a shot-peening treatment for mirror finishing is applied to the surface of the propeller hub 40 and each of the blades 41 of the propeller 21. This shot-peening working for mirror finishing is different from the above-described shot-peening treatment and is a treatment in which composite particles obtained by adhering particulate steel balls to an elastic carrier are blown to the surface of the propeller 21, which is the surface to be worked.

Subsequently, the thus molded propeller 21 is heated at a predetermined temperature for predetermined time, and an oxide coating treatment is then performed with a desired color on the surface of the propeller 21.

As described above, according to the propeller 21 for the outboard motor according to one disclosed embodiment, fatigue strength of the surface of the blade is increased by applying the shot-peening treatment to the blades 41 of the propeller 21, and thus, reduction of thickness and weight of the blades 41 can be realized. Therefore, the performances of the propeller 21 can be improved by alleviating a load to be applied to the power transmission portion such as a shaft and a gear, and durability can be improved by preventing surface deterioration caused by defective casting or erosion, and a manufacturing cost can be reduced by means of improvement of a yield.

Particularly, if the shot-peening treatment is applied to the root portion 43 of the blade 41 of the propeller 21, the root portion 43 of the blade 41 to which the largest load is applied while the outboard motor 1 is driven can be reliably prevented from breaking, and the above-described advantageous effects can be further enhanced.

Moreover, in the case when the shot-peening treatment for mirror finishing is applied to the surface of the propeller 21, there is no concern of occurrence of a crack or erosion caused by a hairline generated on the surface such as observed in the prior-art buffing, and the outer appearance or configuration, operational performance, and durability of the propeller 21 can be improved at the same time.

Furthermore, in the manufacturing process of the propeller 21 for an outboard motor described above, the color of the oxide coating can be made more vivid by applying the shot-peening treatment for the mirror finishing before the oxide coating is applied on the surface of the propeller 21, and merchantability can be further improved.

In another disclosed embodiment, the propeller 21 according to this example of the embodiment has an outer surface covered with a metal material by way of an oxide coating treatment, and the base propeller 21 contains at least one of materials, such as, titanium, stainless steel, and copper, and optionally is formed of titanium.

As described hereinbefore, the propeller 21 for an outboard motor is formed by integrally molding a propeller hub 40 having a double-cylindrical structure formed by integrally joining concentric inner cylindrical body 37 and outer cylindrical body 38 to a plurality of radial ribs 39, and three blades 41 arranged radially on the outer side of the outer cylindrical body 38. A coupling cylinder 42 made of rubber is press-fitted into the inner cylindrical body 37, and the propeller 21 is tightly attached to the propeller shaft 22 by fitting the coupling cylinder 42 in the rear portion of the propeller shaft 22.

The propeller 21 for an outboard motor is manufactured by heating a base member forming the propeller 21 in which the propeller hub 40 and each of the blades 41 are integrally molded by casting at a predetermined temperature for predetermined time and by forming oxide coating on the surface of the propeller. At this time, the color of the oxide coating can be freely changed in compliance with the preference of a user by changing the heating temperature or heating time. Therefore, merchantability of the propeller 21 for an outboard motor can be improved while corrosion resistance and peeling resistance thereof are improved.

Furthermore, in the manufacturing process of the propeller 21 for an outboard motor of the present embodiment, the surface of the propeller 21 may be subjected to mirror finishing by the shot-peening treatment, as described hereinbefore the oxide coating is applied on the surface of the propeller 2, and as a result, the color of the oxide coating can be made more vivid, and merchantability can be further improved.

According to the propeller 21 for an outboard motor according to one disclosed embodiment, the oxide coating in a desired color can be formed on the surface only by heating a propeller or base material thereof at a predetermined temperature for predetermined time, and thus, a propeller with high corrosion resistance and merchantability can be manufactured easily through fewer man-hours and with a lower cost. Moreover, even if the outboard motor 1 rides onto shallow water or is brought into contact with a floating object in the seawater, paint on the propeller 21 does not peel easily and an appearance of the propeller 21 is not damaged.

It is to be noted that the present invention is not limited to the described embodiment and many other changes and modifications or alternations may be made without departing from the scopes of the appended claims.

For example, in the disclosed embodiments, the outboard motor 1 of the type in which exhaust gas of the engine 14 is exhausted to the rear side from a gap between the inner cylindrical body 37 and the outer cylindrical body 38 is described as an example, and thus, the propeller hub 40 has a double-cylindrical structure of the inner cylindrical body 37 and the outer cylindrical body 38, but this disclosed embodiment is only one mode for embodying the invention, and in a case, for example, the exhaust gas of the engine 14 is exhausted from another portion, the propeller hub may be composed of one cylindrical body.

Moreover, it is needless to say that the number and the shape of the blades 41 are not limited to three as mentioned above and other changes may be possibly made. 

1. A propeller for an outboard motor fixed to a rear portion of a propeller shaft pivotally supported in an anteroposterior direction of a hull to which the outboard motor is mounted on a lower portion of the outboard motor, comprising: a cylindrically formed propeller hub; and a plurality of blades provided radially on an outer side of the propeller hub, and having surfaces of the blades to which a shot-peening treatment is applied.
 2. The propeller for an outboard motor according to claim 1, wherein the each of blades has a blade body having a surface of which the shot-peening treatment is applied.
 3. The propeller for an outboard motor according to claim 1, wherein the each of blades has a blade root portion having a surface of which the shot-peening treatment is applied.
 4. The propeller for an outboard motor according to claim 1, wherein the shot-peening treatment for mirror finishing is applied.
 5. The propeller for an outboard motor according to claim 1, wherein the propeller is formed of a metal material having a surface on which an oxide coating is formed by heating the metal material forming the propeller.
 6. The propeller for an outboard motor according to claim 5, wherein the metal member forming the propeller contains at least one material of titanium, stainless steel and copper.
 7. The propeller for an outboard motor according to claim 5, wherein the metal member forming the propeller is subjected to mirror finishing by a shot-peening treatment before the oxide coating is formed. 